1. Field of the Invention
The present invention generally relates to an aluminum bonding member and a method for producing the same. More specifically, the invention relates to an aluminum bonding member, in which a tubular member for allowing the flow of a cooling agent and which is used as a cooling member for electronic parts, such as metal/ceramic circuit boards, and a method for producing the same.
2. Description of the Prior Art
As a conventional method for mounting a cooling member, such as a radiating fin, on a metal/ceramic circuit board wherein a metal circuit plate is bonded to one side of a ceramic substrate and a radiating metal plate is bonded to the other side thereof, there is known a method for soldering one or a plurality of ceramic substrates, to each of which a metal circuit plate having a semiconductor chip soldered thereon is bonded, on a metal base plate (a radiating plate) or a composite material and for mounting a radiating fin on the reverse of the metal base plate or the like via a radiating grease. There is also known a method for bonding a radiating fin to a ceramic substrate via a brazing filler metal (see, e.g., Japanese Patent Laid-Open No. 4-363052). Moreover, there is proposed a method for integrating an electronic circuit board of a ceramic or a composite material of carbon and a metal with a cooling system using a liquid or gas as a cooling medium (see, e.g., Japanese Patent Laid-Open No. 2001-7265).
However, in the conventional method for soldering a ceramic substrate on a metal base plate, heat sink characteristics are deteriorated by the solder, and the thermal conductivity of the radiating grease used for mounting the radiating fin on the metal base plate or the like is a few W/mK which is extremely small, so that there is a problem in that the heat sink characteristics are further deteriorated. In addition, there are some cases where the yield of products may be deteriorated by solder voids. Moreover, the use of a solder containing lead (Pb) goes against a recent tendency to make Pb free in order to prevent environmental pollution.
In the method disclosed in Japanese Patent Laid-Open No. 4-363052, since an air cooling radiating fin is used, the cooling power of the radiating fin is generally lower than that of a water cooling system, so that there is a problem in that it is difficult to stabilize the performance of the radiating fin.
In the method disclosed in Japanese Patent Laid-Open No. 2001-7265, it is possible to substantially solve the above described problem on the deterioration of heat sink characteristics due to the solder and radiating grease, and the above described problem caused by the use of the radiating fin. However, it is required to dig grooves in two preform substrates of a ceramic or the like to sandwich a pipe, which is previously shaped so as to fit in the grooves, between the preform substrates to temporally fix them to put them in a die to inject a molten metal of aluminum or copper into the die to cast a cooling system at a high pressure. Therefore, costs for the die and producing apparatus are relatively high, and there are some cases where it is difficult to enhance the uniformity and working precision of the preform substrates. Moreover, since the porosity of the preform substrates is not less than 5% and is less than 50%, there are some cases where it is difficult to fill a molten metal in the preform substrates to mechanically realize the bonding by the anchor effect.